chapter 1: introduction
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Chapter 1: Introduction. What is an Operating System?. A program that acts as an intermediary between a user of a computer and the computer hardware Operating system goals: Execute user programs and make solving user problems easier Make the computer system convenient to use - PowerPoint PPT PresentationTRANSCRIPT
Silberschatz, Galvin and Gagne ©2009Operating System Concepts – 8th Edition,
Chapter 1: Introduction
1.2 Silberschatz, Galvin and Gagne ©2009Operating System Concepts – 8th Edition
What is an Operating System?
A program that acts as an intermediary between a user of a computer and the computer hardware
Operating system goals: Execute user programs and make solving user problems easier Make the computer system convenient to use Use the computer hardware in an efficient manner
1.3 Silberschatz, Galvin and Gagne ©2009Operating System Concepts – 8th Edition
Computer System Structure
Computer system can be divided into four components Hardware – provides basic computing resources
CPU, memory, I/O devices Operating system
Controls and coordinates use of hardware among various applications and users
Application programs – define the ways in which the system resources are used to solve the computing problems of the users Word processors, compilers, web browsers, database
systems, video games Users
People, machines, other computers
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Four Components of a Computer System
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Operating System Definition
OS is a resource allocator Manages all resources Decides between conflicting requests for efficient and fair
resource use OS is a control program
Controls execution of programs to prevent errors and improper use of the computer
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Operating System Definition (Cont)
No universally accepted definition “Everything a vendor ships when you order an operating system” is good
approximation But varies wildly
“The one program running at all times on the computer” is the kernel. Everything else is either a system program (ships with the operating system) or an application program
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Computer Startup
bootstrap program is loaded at power-up or reboot Typically stored in ROM or EPROM, generally known as firmware Initializes all aspects of system Loads operating system kernel and starts execution
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Computer System Organization
Computer-system operation One or more CPUs, device controllers connect through common bus
providing access to shared memory Concurrent execution of CPUs and devices competing for memory
cycles
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Computer-System Operation
I/O devices and the CPU can execute concurrently Each device controller is in charge of a particular device type Each device controller has a local buffer CPU moves data from/to main memory to/from local buffers I/O is from the device to local buffer of controller Device controller informs CPU that it has finished its operation by causing
an interrupt
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Common Functions of Interrupts
Interrupt transfers control to the interrupt service routine generally, through the interrupt vector, which contains the addresses of all the service routines
Interrupt architecture must save the address of the interrupted instruction Incoming interrupts are disabled while another interrupt is being processed
to prevent a lost interrupt A trap is a software-generated interrupt caused either by an error or a user
request An operating system is interrupt driven
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Storage Structure
Main memory – only large storage media that the CPU can access directly Secondary storage – extension of main memory that provides large
nonvolatile storage capacity Magnetic disks – rigid metal or glass platters covered with magnetic
recording material Disk surface is logically divided into tracks, which are subdivided into
sectors The disk controller determines the logical interaction between the
device and the computer
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Storage Hierarchy
Storage systems organized in hierarchy Speed Cost Volatility
Caching – copying information into faster storage system; main memory can be viewed as a last cache for secondary storage
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Storage-Device Hierarchy
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Caching
Important principle, performed at many levels in a computer (in hardware, operating system, software)
Information in use copied from slower to faster storage temporarily Faster storage (cache) checked first to determine if information is
there If it is, information used directly from the cache (fast) If not, data copied to cache and used there
Cache smaller than storage being cached Cache management important design problem Cache size and replacement policy
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How a Modern Computer Works
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Computer-System Architecture
Most systems use a single general-purpose processor (PDAs through mainframes) Most systems have special-purpose processors as well
Multiprocessors systems growing in use and importance Also known as parallel systems, tightly-coupled systems Advantages include
1. Increased throughput
2. Economy of scale
3. Increased reliability – graceful degradation or fault tolerance Two types
1. Asymmetric Multiprocessing
2. Symmetric Multiprocessing
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Symmetric Multiprocessing Architecture
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A Dual-Core Design
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Clustered Systems
Like multiprocessor systems, but multiple systems working together Usually sharing storage via a storage-area network (SAN) Provides a high-availability service which survives failures
Asymmetric clustering has one machine in hot-standby mode Symmetric clustering has multiple nodes running applications,
monitoring each other Some clusters are for high-performance computing (HPC)
Applications must be written to use parallelization
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Operating System Structure
Multiprogramming needed for efficiency Single user cannot keep CPU and I/O devices busy at all times Multiprogramming organizes jobs (code and data) so CPU always has
one to execute A subset of total jobs in system is kept in memory One job selected and run via job scheduling When it has to wait (for I/O for example), OS switches to another job
Timesharing (multitasking) is logical extension in which CPU switches jobs so frequently that users can interact with each job while it is running, creating interactive computing Response time should be < 1 second Each user has at least one program executing in memory process If several jobs ready to run at the same time CPU scheduling If processes don’t fit in memory, swapping moves them in and out to
run Virtual memory allows execution of processes not completely in
memory
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Operating-System Operations
Interrupt driven by hardware Software error or request creates exception or trap
Division by zero, request for operating system service Other process problems include infinite loop, processes modifying each
other or the operating system Dual-mode operation allows OS to protect itself and other system
components User mode and kernel mode Mode bit provided by hardware
Provides ability to distinguish when system is running user code or kernel code
Some instructions designated as privileged, only executable in kernel mode
System call changes mode to kernel, return from call resets it to user
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Process Management
A process is a program in execution. It is a unit of work within the system. Program is a passive entity, process is an active entity.
Process needs resources to accomplish its task CPU, memory, I/O, files Initialization data
Process termination requires reclaim of any reusable resources Single-threaded process has one program counter specifying location of
next instruction to execute Process executes instructions sequentially, one at a time, until
completion Multi-threaded process has one program counter per thread Typically system has many processes, some user, some operating system
running concurrently on one or more CPUs Concurrency by multiplexing the CPUs among the processes / threads
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Process Management Activities
The operating system is responsible for the following activities in connection with process management:
Creating and deleting both user and system processes Suspending and resuming processes Providing mechanisms for process synchronization Providing mechanisms for process communication Providing mechanisms for deadlock handling
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Memory Management
All data in memory before and after processing All instructions in memory in order to execute Memory management determines what is in memory when
Optimizing CPU utilization and computer response to users Memory management activities
Keeping track of which parts of memory are currently being used and by whom
Deciding which processes (or parts thereof) and data to move into and out of memory
Allocating and deallocating memory space as needed
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Storage Management
OS provides uniform, logical view of information storage Abstracts physical properties to logical storage unit - file Each medium is controlled by device (i.e., disk drive, tape drive)
Varying properties include access speed, capacity, data-transfer rate, access method (sequential or random)
File-System management Files usually organized into directories Access control on most systems to determine who can access
what OS activities include
Creating and deleting files and directories Primitives to manipulate files and dirs Mapping files onto secondary storage Backup files onto stable (non-volatile) storage media
1.26 Silberschatz, Galvin and Gagne ©2009Operating System Concepts – 8th Edition
Mass-Storage Management
Usually disks used to store data that does not fit in main memory or data that must be kept for a “long” period of time
Proper management is of central importance Entire speed of computer operation hinges on disk subsystem and its algorithms OS activities
Free-space management Storage allocation Disk scheduling
Some storage need not be fast Tertiary storage includes optical storage, magnetic tape Still must be managed Varies between WORM (write-once, read-many-times) and RW (read-write)
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Performance of Various Levels of Storage
Movement between levels of storage hierarchy can be explicit or implicit
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Migration of Integer A from Disk to Register
Multitasking environments must be careful to use most recent value, no matter where it is stored in the storage hierarchy
Multiprocessor environment must provide cache coherency in hardware such that all CPUs have the most recent value in their cache
Distributed environment situation even more complex Several copies of a datum can exist Various solutions covered in Chapter 17
1.29 Silberschatz, Galvin and Gagne ©2009Operating System Concepts – 8th Edition
Open-Source Operating Systems
Operating systems made available in source-code format rather than just binary closed-source
Counter to the copy protection and Digital Rights Management (DRM) movement
Started by Free Software Foundation (FSF), which has “copyleft” GNU Public License (GPL)
Examples include GNU/Linux, BSD UNIX (including core of Mac OS X), and Sun Solaris
Silberschatz, Galvin and Gagne ©2009Operating System Concepts – 8th Edition,
End of Chapter 1